This invention relates to coatings applied to surfaces, and, more particularly, to a white coating that aids in controlling the surface temperature of the article to which it is applied and is also sufficiently electrically conductive to dissipate static charge.
Spacecraft such as satellites and deep-space craft are exposed to a wide range of thermal conditions. A side facing the sun is heated by the direct thermal radiation, while a side facing the void of space is cooled rapidly by radiation. Thermal control of the spacecraft is therefore important. Various techniques have been developed to maintain the interior of the spacecraft at a temperature suitable for occupancy by human beings and sensitive equipment.
In one thermal control approach, the external surface of the spacecraft is covered with a white coating that has a low solar absorptance and a high infrared emittance. The coating aids in maintaining thermal control. It must also be stable to the radiation and low-pressure gaseous environment encountered in space without losing its thermal properties by discoloring or otherwise and must be resistant to mechanical damage by micrometeorite impacts. For some applications, the coating must also be sufficiently electrically conductive to dissipate electrostatic charge on the surface of the spacecraft.
Several types of coatings are currently available to meet these various requirements. In one known type of coating, aluminum-doped zinc oxide particles are dispersed in a potassium silicate ceramic matrix that is applied to the surfaces of the spacecraft. This coating, while operable in some situations, tends to be brittle and subject to fracture during curing and handling. The zinc oxide/potassium silicate coating also cannot be applied to thin, flexible article substrates because the coating cracks when the substrate flexes.
In another approach, a two-part coating system is applied to the spacecraft surface. The base coat consists of metallic flakes in a silicone binder to provide electrical charge dissipation. The top coat includes zinc othostannate pigment in a silicon binder to produce low solar absorptance and high infrared emittance. This two-part coating is also usable in some applications, but is difficult to use and produces inconsistent results because of its complexity.
There is a need for a coating for use on spacecraft and in other thermal-control applications. Such a coating should exhibit acceptable thermal and electrical properties, and also be easy to use to produce consistent results. The present invention fulfills this need, and further provides related advantages.